Are you limited to two words? I suggest "News for Managers" as unambiguous and not requiring the possessive apostrophe.

One could also use the plural in a non-possessive sense: "Managers News" (news for managers, in other words). To me, it doesn't feel quite as right. No one but a persnickety copy editor would notice, though.

I like the last option the best. Is "Manager news" completely incorrect also?
– submarinesSep 26 '18 at 14:33

I would not say completely incorrect, but it is singular. A more "plural" wording is "Management News" -- information for people in management, that is, managers -- plural.
– user8356Oct 3 '18 at 17:32